SORBENTS BASED ON THE Ni,Fe-LAYERED DOUBLE HYDROXIDES AND ITS MAGNETIC NANOCOMPOSITES FOR DEACTIVATION AND PRECONCENTRATION OF Cs(I) AND Sr(II) IONS FROM AQUEOUS SOLUTIONS

Abstract

The synthesis and comparative evaluation of the adsorption capacity in relation to Sr(II) and Cs(I) ions of the carbonate form of Ni(II)/­Fe(III)–layered double hydroxides (NiFe-LDH) and their nanocomposites was carried out. At first, Fe3O4 nanoparticles having a crystallite size of 20–50 nm were obtained by Fe(III) precursors. In the second step, Fe3O4 nanoparticles were embedded in NiFe-LDH matrix by the co-precipitation at hydrothermal conditions and subsequent condensation of the basic solution containing Fe3O4nanoparticles. The influence of the physicochemical parameters of the synthesized sorbents on the efficiency of magnetic solid phase extraction of these radionuclides from aqueous solutions was investigated. Their effectiveness in extracting Sr(II) and Cs(I) ions with a change in the pH of the aqueous medium was evaluated, as well as sorption isotherms on the obtained sorbents at pH0 4.5–5.0 were obtained, and their analysis and processing were carried out to establish the mechanism of sorption extraction at all le­vels of filling of the sorption layer with analytes. Equilibrium adsorption data were analyzed using Freundlich and Langmuir isotherm models. Of the models tested, Langmuir isotherm expressions were found to give better fit to the experimental data compared to the Freundlich model. The applicability of mathematical models for estimating the kinetic patterns of sorption of radionuclides on NiFe-LDH and their magnetic nanocomposites was analyzed. The adequacy of the Boyd and Morris – Weber diffusion models in the initial section (up to F = 0.4–0.6) of the kinetic curves is shown. Kinetically, the growth of effective diffusion coefficients and adsorption rate constants is observed in the series: Fe3O4<NiFe-LDH<Fe3O4@NiFe-LDH, and the pseudo-second-order kinetic model most accurately reflects the patterns of sorption of these radionuclides. Due to high sorption efficiency and manufacturability, the obtained sorbents are promising for water purification from radioactive pollutants.